1. Field of the Invention
The present invention relates to a method of manufacturing large area graphene, and the resulting graphene-based photonics devices, which are used in a variety of applications.
2. Description of the Related Art
A Laser Imaging and Detection and Ranging (LIDAR) system is a remote sensing technology that provides for the detection, identification, and the precision measurement of the range of a target in military missions, using a laser to illuminate the target and analyze the reflected light. The components of a scanning LIDAR system include a laser, a scanner and optics (i.e., oscillating plane minors, a combination with a polygon mirror, a dual axis scanner etc.), photodetectors and receiver electronics, and position and navigation systems (i.e., Global Positioning System (GPS) and Inertial Measurement Unit (IMU)). Typically, a laser with shorter pulses achieves better target resolution, provided the LIDAR receiver detectors and electronics have sufficient bandwidth. With respect to photodetectors, solid state photodetectors, such as silicon photodiodes are used.
Currently, photon-counting detectors do not really exist for wavelengths beyond 1 μm. LIDAR sensors require high bandwidth and low-noise photodetectors operating in the 1-1.6 μm near-infrared (NIR) wavelength regions. Silicon (Si) photodetectors do not meet these requirements since they have poor quantum efficiency for wavelengths greater than 1.1 μm and have low bandwidth, such as <500 MHz.
Currently, the dominant method to generate ultrafast laser pulses passively is the use of semiconductor saturable absorber minors (SESAMs), which is a mirror structure with an incorporated saturable absorber made with semiconductor technology. SESAMS are used for the generation of ultrashort pulses by passive mode locking of various types of lasers. Typically, a SESAM contains a semiconductor Bragg mirror and (near the surface) a single quantum well absorber layer. The materials of the Bragg mirror have a larger bandgap energy, so that essentially no absorption occurs in that region. Such SESAMs are sometimes also called saturable Bragg reflectors (SBRs). For obtaining a large modulation depth, as required—e.g., for passive Q-switching using Q-switched lasers—a thicker absorber layer can be used. Also, a suitable passivation layer on the top surface can increase the device lifetime. This type of passive mode locker produces exceptional results but is difficult to fabricate, expensive and limited to bandwidth.
Further, other potential remote sensing instruments with requirements to perform spectroscopic measurements, such as those using methane, need specific wavelengths most likely in the mid-infrared (IR) to long-wave IR (LWIR) bands, to match the absorption spectra of the species being studied, which are difficult to provide. Current spectroscopic techniques which offer broadband, high-resolution capability, require cumbersome optics with moving parts and/or sophisticated cryogenic cooling to obtain the necessary resolving power and sensitivity, and thus, are not suitable for air or space vehicle applications whose platforms require strict size and weight requirements. Further, commercial charge-coupled device (CCD) spectrometers are not available in the terahertz spectral range, and which can operate at room temperature.
Accordingly, an ultrafast photodetector and mode lock device for a laser transmitter which can bridge the gaps for high speed, highly sensitive detection from NIR to LWIR, in a remote sensing device, which is easy to produce, is needed. In addition, a tunable terahertz (THz) or sub-millimeter detector that can operate at room temperature would be advantageous.